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Hi, I don't know if this is the correct place to post this question.

(Admin edit: I moved this to it's current location)

On my 78 900 GTS the tachometer started to act very strange. At 4k rpm or so, the needle is dancing all over the place. When at idle it works fine. Any guess on where to start to check it? Any known issues that could short-cut my diagnose time?

Thanks

Ramon

I would start with the easy things first. The end of your cable goes to the front bevel drive cover. Carefully unscrew the cable from here and have a look at the cable drive. From memory the cable has a square end and fits into the tacho drive. Make sure the cable is actually engaging in the drive. By the symptoms you describe the cable end may not be positively engaged with the drive. You could maybe remove the cable from the tacho end and try twisting it while its engaged at the drive end. Try visa versa to make sure its engaging at the tacho end.

If you have no joy there, 3 screws guard the entrance to the forward bevel cover and the tacho drive within. Inside there is a drive peg. Make sure everyone is happy in there. It`s fairly self explanatory once your in there. If there is no fault there either it may be in the instrument itself. By my experience the Veglia gauges are quite reliable. I have seen the Smiths give trouble however.

Oh, forgot to mention. If you do do into the front bevel cover, make very sure that the drive peg and little locating sleeve are securely in place and can't escape. You`ll see what I mean if you go in there. If the drive peg escapes while running it could be pretty catastrophic to your cam timing............and your wallet. Once again, its fairly simple.You will see what mean if you go in there.

Sounds like the cable needs cleaning and lubrication, cable binding in the housing. It twists when turning and unwinds suddenly. If you use light grease, lube cable except for the last 3 or so inches on the meter end as the grease can walk up the cable as it turns and foul the meter.

Thanks to all.

For now I lubed the cable to see if it gets better. Hardest part was fighting the rubber boot. How you guys take that off? It’s just so hard.

Thanks again.

I concur with the above and especially the cable end possibly being rounded off. Check this first as noted.

Next, remove the cable from gauge and tach drive. I suggest you first pull inner cable from outer and clean it. Then spray cleaner down inside housing and put inner cable back in there and do a push/pull a hundred times while continuing to spray cleaner in there. Remove inner and wipe, etc. now lube inner cable and reinsert - the end with the swaged stopper goes on the top (gauge end).